1. Field of the Invention
The present invention relates to a porous hydrogen separation membrane. More specifically, the present invention relates to a hydrogen separation membrane, capable of simultaneously solving a problem of low hydrogen permeability exhibited by a conventional palladium-based dense separation membrane and a problem of hydrogen embrittlement (HE) exhibited by a stainless steel support, and a method for preparing the same.
2. Description of the Related Art
A great deal of research and study has been made into a process for producing hydrogen via reforming of hydrocarbon, and such attempts are still being actively undertaken. According to a process for producing syngas from hydrocarbon, hydrogen, which is used as a source gas of Polymer Electrolyte Membrane Fuel Cell (PEMFC), is produced via steam reforming and water gas shift reaction (i.e., reaction of carbon monoxide with water), as shown in the following reactions 1 and 2 (A. Basile, L. Paturzo, An experimental study of multilayered composite palladium membrane reactors for partial oxidation of methane to syngas, Catalysis Today 67 (2001) 55):CH4+H2→CO+3H2, ΔH°298=+206 kJ/mol  (Reaction 1)CO+H2O→CO2+H2, ΔH°298=−41 kJ/mol  (Reaction 2)
Hydrogen generated in a reactor can force the backward water-forming reaction depending upon concentrations of carbon monoxide and hydrogen and thus the reverse reaction may proceed toward regeneration of methane. As a conversion rate of methane is dependent upon temperatures and removal of hydrogen from the reaction chamber further enhances the conversion rate of methane, thus it is possible to lower an operating temperature of the reactor.
At present, a great deal of research into development of palladium-based dense separation membranes, and porous separation membranes utilizing zeolite or gamma-alumina has been actively undertaken (R. Cheechetto, N. Bazzanella, B. Parron, A. Miotello, Palladium membranes prepared by RF magnetron sputtering for hydrogen purification, Surface and Coatings Technology 177-178 (2004) 73); and T. Tomita, K. Nakayama, H. Sakai, Gas separation characteristics of DDR type zeolite membrane, Microporous and Mesoporous Materials, 68 (2004) 71).
The palladium-based dense separation membrane provides a high degree of separation as it performs a separation process via conduction of hydrogen ions, while suffering from disadvantages such as low hydrogen permeability per unit area, very complicated manufacturing processes, and in particular, hydrogen embrittlement (HE) when using stainless steel-based metal supports. Therefore, intensive efforts have been made to secure durability of the membrane (D. Lee, Y. Lee, S. Nam, B. Sea, K. Lee, Preparation and characterization of SiO2 composite membrane for purification of hydrogen from methanol steam reforming as an energy carrier system for PEMFC, Separation and Purification Technology 32 (2003) 45). In contrast, as the porous separation membrane can provide high hydrogen permeability, it is expected that such a porous separation membrane is applicable to systems in which process configuration can be implemented even at low selectivity, as in processes for producing hydrogen as a source gas for fuel cells.
However, most porous separation membranes, which have been investigated or developed hitherto, employ ceramic-based (gamma alumina, zeolite) supports (D. Lee, L. Zang, S. T Oyama, S. Niu, R. F. Saraf, Synthesis, Characterization, and gas permeation properties of a hydrogen permeable silica membrane supported on porous alumina, J. Membrane Science 231 (2004) 117). In this connection, the most important disadvantage of the separation membranes using ceramic-based supports consists in difficulty of systemization of the completed separation membrane. That is, for multi-layer configuration of the separation membrane, there is a need for construction of the system via sealing and welding, but there still remains substantially no development of technologies for such a purpose until now.